Use of a Variable Rate Spray Bar to Minimize Wheel Path Bleeding for Asphalt-Rubber Chip Seal Applications

Chip seals constructed in areas with a combination of high truck traffic volume and high climatic temperatures are susceptible bleeding in the wheel paths and raveling in nonwheel path areas. These failures arise from inherent differences in traffic loading in the two areas. Addressing this problem calls for the binder application rate for the two regions to be varied and using asphalt binders with a high stiffness at high temperatures to prevent bleeding. No well-established design methods that yield a different binder application rate exists. Although equipment for applying variable binder rates exists, there is limited performance data, and no guidelines for calibrating the equipment in the field exist. This paper presents the findings of field studies in which both uniform and variable application rates were used to construct asphalt-rubber chip seals in California. The results show that using different binder application rates in and out of wheel paths can mitigate bleeding and raveling. The paper also presents a new field calibration test method for both conventional and variable rate distributor spray bars.